Sliver of hope for oyster farmers and our fish

IN SPITE of awful water quality, oyster farmers on the Richmond River are still hoping for a reason to come up smiling one day – and perhaps they’ve found it.

By Tony Zann

About 20ha of oyster leases on the Richmond once were capable of producing a around 800,000 oysters a year, along with 12 to 15 human jobs and food and habitat for an extraordinary number of marine species.

With each 5cm oyster sieving more than 70 litres of water a day, the rock walls and oyster racks of the lower river also acted as a massive filter for the Richmond. No longer.

Now, thanks to acid runoff from drained wetlands, dissolved oxygen crashes and excessive siltation brought on by a century of poor farming practices, few oysters are likely to live to maturity.

Since 1976 all serious attempts at farming on the Richmond have failed, with local farmers now importing oysters from other systems and growing them out during rare times of acceptable water quality.

Even the toughest of Sydney rock oysters, selectively bred in 2016 by the Department of Primary Industry at Port Stephens to resist the deadly QX disease, appear doomed.

The Richmond River chapter of national angler conservation group OzFish Unlimited volunteered to supervise the trials of these oyster strains. Ballina’s commercial mullet netters paid for the oyster-farming hardware from their river futures fund.

Sadly, after 20 months, one batch of 3000 of a resilient test strain is now down to a mere 50 oysters, while among a tougher strain, 132 of 3000 remain alive. So both show a 96-98 per cent mortality and the survivors aren’t expected to make it to next July, when it was hoped they would reach market size.

The control strain of 3000 “standard” oysters all died more than a year ago.

But hope is not lost.

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In January 2017, while repairing his disease-devastated lease, one of the Richmond’s remaining farmers noticed a single live oyster among all the dead shells. Its exterior had a crescent-shaped blotch and soon the grower noticed a few more live oysters with similar “smiley face” markings.

He advised OzFish Richmond, who contacted Dr Wayne O’Connor, of DPI’s shellfish research division at Port Stephens. He requested samples.

Of the 60 samples sent, there were only two male oysters, but enough to provide fertilise about 40 females. Three weeks later, 50,000 oyster larvae began to settle into the research tanks as hard-shelled “spat”.

These appear to be a different species to the conventional Sydney rock.

“There are a number of oyster species found in NSW and reports of naturally occurring oysters that differ in appearance and seem to be surviving disease outbreaks in the Richmond River have peaked our interest,” Dr O’Connor said.

“While we are looking closely at the genetics of these oysters, we have been able to produce some in the hatchery so that we can fast-track assessments of their performance back in the river.

“Thanks to OzFish and the local farmers for bringing these oysters to our attention and facilitating this work.”

A few weeks ago, OzFish deployed 10,000 juvenile spat into a Richmond Oysters lease in Mobbs Bay in the hope that they may survive in the turbid waters of the Richmond.

OzFish Richmond chair John Larsson said, “Mobbs Bay will be a real test for these oysters, given questionable water entering from the adjacent drain.

“But their parents came from one of the retaining walls a few hundred metres away, so we’re hoping these young ones will show the same fighting qualities so they can return some of the benefits that oysters bring to any healthy estuary.”

A large number of these young oysters already display that same crescent-shaped “smiley” blotch on the outer shell over the adductor muscle.